Aliphatic polyesters such as polylactic acid are used for producing biodegradable moldings, as for example packaging films for the food industry. Polylactic acid, however, can also be spun to form fibers, and is therefore employed as pillow filling, carpet fibers, and cosmetics wipes. A problem is the brittleness of aliphatic polyesters.
WO 96/31561 A1 addresses the unsatisfactory materials properties obtained when aliphatic polyesters are used to produce biodegradable moldings. Proposed accordingly are mixtures, based on starch, which additionally comprise at least one further biopolymer, examples being aromatic polyesters, polyesteramides. Mixtures of polylactic acid with starch, plasticizer, and a thermoplastic polymer, such as polyvinyl alcohol or ethylene-vinyl alcohol copolymers, are proposed in WO 98/40434 A1. WO 2005/059031 proposes improving the properties of moldings based on polylactic acid by adding a crosslinkable impact modifier. A proposed impact modifier is an ethylene-(meth)acrylate copolymer which comprises (meth)acrylate units with epoxy groups. US 2008/0188597 A1 describes mixtures for producing biodegradable moldings that comprise as their biodegradable component aliphatic polyesters, more particularly polylactic acid. For the purpose of improving the mechanical strength, the aliphatic polyesters are blended with a thermoplastic having a relatively high Tg of ≦80° C., such as polystyrene or PMMA, for example. To improve the flame retardation, an organic phosphoric acid is added. WO 2006/074815 A1 proposes improving the properties of the end products and avoiding the costly and inconvenient preliminary drying of polylactic acid before its thermoplastic processing by using aliphatic polyesters such as polylactic acid in a mixture with aliphatic-aromatic polyesters, and, more particularly, using epoxide crosslinkers as well, such as epoxy-functional polymers or bisphenol A epoxides. U.S. Pat. No. 5,726,220 proposes producing biodegradable moldings from a mixture of polylactic acid with ethylene-vinyl acetate copolymer.
A problem affecting the blending of polylactic acid with other, more flexible biopolyesters and/or thermoplastics is the unsatisfactory miscibility of the individual components.
The object was therefore to provide compositions based on aliphatic polyesters, more particularly polylactic acid, which are distinguished not only by good processing properties but also by improved mechanical